Comparing Topologies

It's possible that a set $X$ can be endowed with two or more topologies that are comparable. Over the years, mathematicians have used various  words to describe the comparison: a topology $\tau_1$ is said to be coarser than another topology $\tau_2$, and we write $\tau_1\subseteq\tau_2$, if every open set in $\tau_1$ is also an open set in $\tau_2$. In this scenario, we also say $\tau_2$ is finer than $\tau_1$. But other folks like to replace "coarser" by "smaller" and "finer" by "larger." Still others prefer to use "weaker" and "stronger." But how can we keep track of all of this? Personally, I like to think in terms of (and while sipping a cup of) coffee!

(Now does it make sense why the indiscrete topology on a set $X$ is the coarsest/smallest/weakest topology, while the discrete topology is the finest/largest/strongest topology? )

Related Posts

Need to Prove Your Ring is NOT a UFD?

The Back Pocket

Operator Norm, Intuitively

The Back Pocket

Two Ways to be Small

The Back Pocket

Completing a Metric Space, Intuitively

The Back Pocket
Leave a comment!